Interfacial Rheology of Complex Fluids

Interfacial rheology is concerned with the deformation and flow of fluid–fluid interfaces laden with surface-active moieties such as polymers, proteins, particles and surfactants. Unlike bulk rheology, interfacial measurements focus on the two-dimensional network formed at the boundary between immiscible phases, where lateral interactions and adsorption kinetics give rise to complex viscoelastic responses under shear and dilatational deformations. Research in this field seeks to elucidate how interfacial structure—from monolayers to particulate films—governs macroscopic properties in emulsions, foams, coatings, pharmaceutical formulations and biological systems. Recent advances have revealed dynamic heterogeneity arising from interfacial structural disorder, nonlinear stress responses under large-amplitude oscillations and the intricate coupling between bulk and surface flows. Such insights underpin the optimisation of formulation stability, targeted drug delivery, enhanced oil recovery and the design of stimuli-responsive materials. Multiscale experimental techniques, complemented by computational models, now enable real-time probing of interfacial complex moduli, the separation of elastic and viscous contributions, and the prediction of flow-induced changes in surface microstructure. This convergence of theory, experiment and simulation is forging a comprehensive framework for the rational design and control of complex fluid–fluid interfaces.

Research from Nature Portfolio

Studies have demonstrated that complex interfaces formed by proteins, polymers and nanoparticles exhibit pronounced dynamic heterogeneity, with relaxation responses best described by stretched-exponential kinetics. These interfaces display asymmetry between expansion and compression deformations, indicating that interfacial structural disorder governs relaxation pathways. Investigations combining step deformations, atomic force microscopy and molecular simulations have shown that momentum transfer between bulk and interface plays a dominant role, challenging the traditional view of homogeneous two-dimensional viscoelastic films. Such work establishes that many complex interfaces behave more like disordered viscoelastic solids than as uniform interfacial liquids, necessitating revised constitutive models for accurate prediction of interfacial flow phenomena.

Interfacial Rheology of Complex Fluids publication trend

The graph below shows the total number of articles in interfacial rheology of complex fluids across all publications each year (not limited to Nature Index journals).

Technical terms

Interfacial rheology: Study of deformation and flow characteristics of fluid–fluid interfaces bearing surface-active layers.

Dilatational modulus: Measure of interfacial resistance to changes in surface area, combining elastic and viscous effects (dγ/dlnA).

Surface shear viscosity: Quantification of interfacial resistance to tangential shear deformations.

Dynamic heterogeneity: Spatial and temporal variation in relaxation behaviour due to structural disorder within interfacial layers.

Large-amplitude oscillatory dilatation (LAOD): Oscillatory deformation of an interface with amplitudes large enough to induce nonlinear viscoelastic responses.

References

1. Surface stress decomposition in large amplitude oscillatory interfacial dilatation of complex interfaces. Journal of Colloid and Interface Science (2023).
2. A Study on the Dilational Modulus Measurement of Polyacrylic Acid Films at Air–Water Interface by Pendant Bubble Tensiometry. Polymers (2024).
3. Dynamic heterogeneity in complex interfaces of soft interface-dominated materials. Scientific Reports (2019).